1. Field of the Invention
The present invention relates to a trochoidal pump comprising an inner rotor and an outer rotor having a trochoidal toothed shape, wherein noise caused by pulsation generated when a fluid is discharged can be reduced.
2. Description of the Related Art
A trochoidal pump is widely used as a lubricating oil pump fitted in an automobile engine, or the like. This trochoidal pump is fitted with an inner rotor and an outer rotor having a trochoidal toothed shape. Utility Model No. (Sho)64-56589 discloses a trochoidal pump of this kind, having a composition wherein the rear side face of each tooth of the inner rotor in the direction of rotation is formed into a simple arc about a single central point, and the height of this section is made lower than the tooth shape based on the trochoidal curve.
Furthermore, Japanese Patent Laid-open No. (Hei)2-95787 discloses a pump wherein the faces of the tips of the inner teeth of the outer rotor and the outer teeth of the inner rotor are formed so as to follow a partial circumference of a circular cylinder drawn about the centre of rotation of the respective rotor, the interval between the front ends of the teeth of the inner rotor and the outer rotor, in other words, the tip clearance, which has an effect on the sealing properties, being maintained at a prescribed value, whilst the front faces of the rotor teeth are adjusted. The two foregoing patents specify the shape of the teeth in such a manner that a prescribed tip clearance is set, equally for each of the teeth.
The foregoing disclosures propose devices wherein the shape of the teeth is changed in order to set a prescribed tip clearance equally for each of the teeth, thereby reducing the pulsation of the fluid, reducing the noise, and also increasing the pump performance. Although the noise is certainly restricted by reduction of fluid pulsation, in reducing the pulsation, the state where the fluid is enclosed in the spaces between the inner rotor and outer rotor is eliminated, and furthermore, it becomes necessary to provide a tip clearance between the ends of the teeth of the inner rotor and the outer rotor, in such a manner that the fluid can be introduced into the spaces and expelled therefrom, smoothly and readily.
By setting this tip clearance to a suitable value, it is possible to reduce pulsation and hence to reduce noise. However, increasing the tip clearance simultaneously produces a drawback in that pump performance declines. Moreover, if the tip clearance is set to a small value in order to maintain pump performance, it then becomes difficult to reduce pulsation and noise. It is extremely hard to set up optimum conditions whilst resolving these mutually contradictory conditions.
The prior art technology sets the same prescribed tip clearance equally for each of the respective teeth, and therefore the setting of the tip clearance is important, but since this tip clearance is set uniformly at the respective teeth of the inner rotor and outer rotor when the pump rotates, a systematic pulsation is generated by the uniformly established tip clearances. When the pressurized fluid generating this systematic pulsation is discharged from the pump, resonance is liable to occur in both the pump and the fluid supply device, and it becomes difficult to prevent the generation of noise. The object of the present invention lies in reducing pulsation of this kind whilst at the same time maintaining pump efficiency at a uniform level.